Serratia species, especially Serratia marcescens, are opportunistic Gram-negative bacilli associated with hospital-acquired infections and increasing antimicrobial resistance. These organisms are capable of causing severe systemic infections, including sepsis and septic shock, particularly in immunocompromised individuals or patients undergoing invasive medical procedures.
Microbiological Profile of Serratia marcescens
Serratia marcescens is a facultatively anaerobic, motile bacillus in the Enterobacteriaceae family. It is a known producer of the red pigment prodigiosin and thrives in moist hospital environments, including respiratory therapy equipment, IV fluids, catheters, and antiseptic solutions.
Key Characteristics:
- Oxidase-negative
- Lactose non-fermenter
- Produces biofilms on indwelling devices
- Natural resistance to several beta-lactams due to AmpC β-lactamase production
Risk Factors for Serratia Sepsis
- Prolonged ICU admission
- Use of mechanical ventilation
- Indwelling devices (catheters, central lines)
- Previous antibiotic exposure, particularly cephalosporins
- Hematologic malignancies or neutropenia
- Renal replacement therapy or dialysis
Pathophysiology of Sepsis Caused by Serratia
Serratia organisms enter the bloodstream via contaminated medical devices or invasive procedures. The progression to sepsis is driven by a systemic inflammatory response triggered by endotoxins (lipopolysaccharides), leading to:
- Endothelial injury
- Coagulation cascade activation
- Microvascular thrombosis
- Hypotension and multiple organ dysfunction
Clinical Manifestations of Serratia Sepsis
- High-grade fever or hypothermia
- Tachypnea, tachycardia
- Hypotension
- Altered sensorium
- Signs of primary infection source (e.g., pneumonia, urinary tract infection, wound infection)
Diagnostic Evaluation and Microbial Identification
Laboratory Investigations
- Complete blood count: Leukocytosis or leukopenia
- Serum lactate and procalcitonin: Assess severity
- Blood cultures: Essential for pathogen isolation
- Urine, sputum, wound cultures: To identify infection source
- Antimicrobial susceptibility testing: Crucial due to emerging resistance
Imaging and Source Detection
- Chest X-ray / CT: Pulmonary infiltrates in ventilator-associated pneumonia
- Abdominal CT: Abscess or intra-abdominal source
- Ultrasound: Catheter-associated infections
Antimicrobial Resistance in Serratia Infections
Serratia marcescens exhibits both intrinsic and acquired resistance mechanisms:
Common Resistance Mechanisms:
- AmpC β-lactamase production: Resistance to penicillins, first- and second-generation cephalosporins
- ESBLs (Extended-Spectrum β-Lactamases): Resistance to third-generation cephalosporins
- Carbapenemase production (e.g., KPC, NDM): Emerging threat in hospital settings
- Efflux pumps and porin mutations: Contribute to fluoroquinolone and aminoglycoside resistance
Treatment Strategies for Serratia Sepsis
Empiric Antibiotic Therapy
Empiric regimens must consider hospital antibiograms and risk of resistance:
- Piperacillin-tazobactam
- Cefepime
- Meropenem (especially in high-risk or ICU patients)
Definitive Therapy Based on Susceptibility
| Resistance Type | Recommended Treatment |
|---|---|
| Non-ESBL-producing | Cefepime, Piperacillin-tazobactam |
| ESBL-producing | Carbapenems (e.g., Meropenem, Ertapenem) |
| Carbapenem-resistant | Ceftazidime-avibactam, Meropenem-vaborbactam, Colistin |
Note: Monotherapy may be inadequate in MDR cases—consider combination therapy and infectious disease consultation.
Duration of Antibiotic Therapy
- Uncomplicated bacteremia: 7–10 days
- With deep-seated infection (e.g., pneumonia, abscess): 10–14+ days
- Persistent bacteremia or endocarditis: 4–6 weeks
Tailor therapy based on clinical resolution, normalization of inflammatory markers, and source control efficacy.
Source Control and Supportive Care
- Remove infected devices (e.g., catheters, central lines)
- Drain abscesses or infected collections
- Provide hemodynamic support with fluids and vasopressors if needed
- Monitor for organ dysfunction and support systems accordingly
Prevention and Infection Control Measures
- Hand hygiene and barrier precautions
- Sterile insertion and maintenance of medical devices
- Routine disinfection of respiratory and dialysis equipment
- Antibiotic stewardship to prevent resistance emergence
Prognosis and Outcome Predictors
Mortality and Morbidity
- Overall mortality for Serratia sepsis ranges between 20%–40%
- Higher in MDR strains and patients with delayed therapy initiation
Poor Prognostic Indicators
- Delayed initiation of appropriate antibiotics
- Immunosuppression or neutropenia
- Septic shock on admission
- Multiorgan failure
Advancements in Serratia Sepsis Management
- Rapid diagnostic tools (PCR, MALDI-TOF) improve early identification
- New antimicrobials such as cefiderocol show promise against MDR isolates
- Phage therapy and immunomodulation are under clinical investigation
Sepsis caused by Serratia demands prompt recognition, accurate diagnosis, and tailored antimicrobial strategies to reduce mortality and complications. The increasing prevalence of multidrug resistance requires coordinated infection control and innovative therapeutic approaches to ensure optimal patient outcomes in intensive care and inpatient settings.
